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We present a near-single-cycle near-infrared light source that can be focused to relativistic intensity at 1kHz. We observe first experimental indications of light waveform effects in laser-wakefield acceleration of relativistic energy electrons

When light sources approach the single cycle limit, both their dispersion compensation as well as pulse characterization become increasingly challenging. As all pulse characterization methods rely on some optical non-linearity, concomitant phase matching issues or dispersive broadening inside the nonlinear medium may severely corrupt the measurement result. One of the best suited methods for characterizing sub-2-cycle pulses is the dispersion scan (d-scan) technique that traditionally relies on second harmonic generation (SHG) as the nonlinear interaction [1]. However, using frequency conversion as a nonlinearity phase matching is the dominant limitation obscuring smaller propagation effects. By using cross-polarized wave (XPW) generation [2] in the d-scan arrangement [3], where no frequency conversion takes place, the phase matching issues are eliminated, uncovering the dispersion and self-phase modulation (SPM), inherently present in the propagation.

To obtain short duration electromagnetic signals, the carrier frequency of the waves has to be increased. The first few cycle electromagnetic waves in the optical domain, that is laser pulses lasting less than 10 fs, were generated in the late 80s'. At the turn of the century, a train of attosecond pulses was first demonstrated, now in the soft X-ray regime.

Summary form only given. The Attosecond Light Pulse Source (ALPS) is one of the four pillars of the Extreme Light Infrastructure (ELI)-the ambitious pan-European laser research project. The major mission of the ELI-ALPS facility is to make a wide range of cutting-edge ultrafast light sources available to the international scientific community.

Summary form only given. We present the current development of an injector for a high-contrast, ultrashort laser system devoted to relativistic laser-plasma interactions at kHz repetition rate [1]. The front-end is based on a 1 kHz, CEP-stabilized Ti:Sa CPA, delivering 1.4 mJ, 28 fs pulses, followed by a cross-polarized wave (XPW) filter for temporal cleaning and shortening. This filter is an optimized version of the waveguided XPW device described in [2]. 300 μJ pulses are routinely generated, corresponding to a XPW internal efficiency as high as 33% and a global energy transmission of 22%. As shown in Fig. 1(a), the XPW filter broadens and shapes the initial amplifier spectrum into a perfectly Gaussian spectrum with 110 nm FWHM, which supports sub-10 fs pulse duration (8.5 fs FTL) This corresponds to a 2.8 temporal pulse shortening factor. The significant spectral broadening and reshaping during XPW arise from the combination of high efficiency and optimized input spectral phase. Accurate characterization highlights the fidelity of the proposed injector. Despite the fact that the spectral broadening is due to nonlinear effects, short-term spectral stability is not degraded after XPW and remains below 2% rms across the entire spectrum (acquisition of 500 consecutive spectra). The long-term spectral stability was monitored by recording the spectrum at regular intervals over 90 min, showing only minor variations. We also measured the excellent spatial quality of the output beam, with a shot-to-shot beam pointing stability of 30 μrad (8 μrad rms). Furthermore, long-term energy stability is monitored continuously and is below 3% rms after the XPW stage. Finally, the measured CEP drift is 170 mrad rms (Fig. 1d). Although slightly higher than the amplifier (typically 110 mrad rms), this value confirms the robustness of the XPW filter. We also study the complex spatio-temporal dynamics of pulse shortening and spectral broadening during the XPW process. This intensity-dependent feature first affects the spectral homogeneity of the XPW beam (Fig. 1b). We highlight the role of self-phase modulation and self-focusing undergone by the fundamental beam and the mechanisms leading to spectral homogeneity of the XPW beam in the far-field (Fig. 1c). The experimental results are supported by 3D calculations. To conclude, our work shows that XPW can be configured to act as a robust pulse cleaning and shortening device, producing sub-10 fs pulses with exceptional spatio-temporal fidelity.

High-harmonic generation (HHG) from solid targets driven by ultra-high-intensity lasers is predicted to be a source of attosecond XUV pulses with shorter wavelengths and higher energies than those currently generated in gases [1,2]. A much less explored regime consists in focusing few-cycle pulses down to wavelength-limited spot sizes in order to reach the ultrahigh intensities using mJ pulse energies. This enables HHG from solid targets using waveform-controlled few-cycle pulses readily obtainable from compact kHz laser systems. Here, we show the first experimental demonstration of HHG from solid targets using intense CEP-controlled two-cycle laser pulses.

Cross polarized wave generation (XPW) is a well established technique for contrast enhancement of ultrashort pulses in high energy laser systems [1]. Efficient conversion with XPW only occurs at high intensities. Weaker, unconverted pre and post pulses are thus rejected by the second polarizer, thereby improving the temporal contrast of the pulse. XPW has several drawbacks especially in terms of simultaneously achieving high conversion efficiencies and output energies. Limitations in seeding the nonlinear filter with high energies arise from the upper intensity limit of white light generation while high conversion efficiencies require excellent beam quality.

Efficient pulse post-compression in a standard hollow-core fiber (HCF) device is proposed, resulting in the routine generation of 4.8 fs, 1.6 mJ pulses with hour-long CEP control from 3.1mJ input pulses. The employed laser system produces 3.1 mJ, ∼25 fs, 1 kHz, carrier-envelope phase (CEP) stable pulses [1]. The compressor device is a 1m-long, 250 µm inner diameter HCF filled with a static pressure of Helium (∼2 bars). The intrinsic throughput of the HCF without gas is 80%.

We present a femtosecond Optical Parametric Amplificator (OPA) which was conceived to perform surgical interventions on eyes using eye-safe wavelengths. It is pumped by a Ti: sapphire laser emmiting 50 fs pulses at 820 nm and at a repetition rate of 1 kHz. A particular effort was made to obtain a very flat and efficient gain spectrum especially around degeneracy. An OPA scheme using consecutively β-BaB 2 O 4 (BBO) crystal and BiB 3 O 6 (BiBO) provides the required behaviour (figure 1). While most OPA are composed of identical crystals on all stages, the originality of our configuration consists in combining the advantages of two different crystals.

Sub-5fs pulses are generated at the mJ level through a hollow-core fiber seeded with circularly polarized pulses. The preservation of carrier-envelope phase of the hollow-core fiber compressor is also demonstrated.

We demonstrated the Mazzler with XPW filter approach to obtain ultrashort pulses with Gaussian shape at the output of the laser system. This scheme can be scaled to higher output energy and sub 10 fs pulses.

A different and highly robust scheme is described in which optimization of the pulse compression involves a distinct sequential two plasma-filament structure, and where the dynamics coincide with a blue-shifted compressible tail on-axis, and a red-shifted background. During the first filament, the spectra is broadened off-axis due to the off-axis peak intensity. The formation of the second filament coincides with a dramatic collection of blue-shifted frequencies on-axis, which form the highly compressed pulse. It is shown that this spatio-spectral-shaping is dramatic in the formation of the second plasma filament.

We demonstrate filamentation at 2 μm using carrier-envelope phase (CEP) stabilized 55 fs, 330 μJ pulses from an OPA. The ultra-broadband output is self-compressed below 3-optical cycles with 270 μJ and preserves the CEP offset.

We present the design of a single ultra intense laser beamline delivering 25PW pulses at one shot per minute as a first step of an ultra intense high field science European project (extreme light infrastructure).

We demonstrate theoretically and experimentally a robust method based on sequential filamentation to optimize compression of high-energy pulses in gases. We gain insight into this process by comparing compression dynamics for linear- and circularly-polarized pulses.

We demonstrate filamentation at 2 mum using carrier-envelope phase (CEP) stabilized 55 fs, 330 mui pulses from an OPA. The ultra-broadband output is self-compressed below 3-optical cycles with 270 muJ and preserves the CEP offset.

We demonstrate a dispersion-free split mirror interferometric autocorrelator suitable for measuring pulses with durations from hundreds of attoseconds to tens of femtoseconds and spectral content from the near-UV to near-IR.

The combination between both OPCPA and conventional amplification techniques is a hybrid scheme that takes advantage of the large, broadband single-pass gain provided by the non-linear parametric interaction as well as the large bandwidth achievable in low-gain Ti:S multipass amplifiers. We investigated different configurations with different spectral bandwidths of the pump beam. The second setup makes use of a 2.5 nm spectrum and a 400 /spl mu/J blue pump pulse energy which gave us the largest amplified spectrum: 120 nm, double the width of the spectrum produced by the oscillator.

We study the temporal and spectral behaviour of high order harmonics generated by pulses with temporally modulated polarization. We observe a harmonic temporal confinement and a harmonic spectral broadening, compatible with 1-or-2 attosecond pulse emission.

We report the self-compression of linearly and circularly polarized light pulses down to the few-cycle regime by self-guided beam propagation of intense 38-fs pulses in different gases with uniform density and with a pressure gradient.

We present temporal characterization of attosecond pulse trains generated during self-guided propagation of intense pulses in a long gas target. Spectral phase jumps are observed, affecting the temporal shape of the attosecond pulse train.

We modulate temporally the polarization of a - 30 fs, SO0 nm IR pulse and use it to generate high order harmonics. The harmonic emission can clearly be confined and the XUV pulse duration can be continuously tuned from - 5 - 7 fs to 50 fs. There are curently two ways to generate a single sub-femtosecond pulse via high order harmonic emission (HHG). The first one is to use ultrashort linearly polarized pulses and to confine the harmonic emission to that of the cutoff harmonics. The second one, valid for plateau harmonics also, is to use a relatively long pulse (-15 fs) and to temporally modulate its polarization. By performing two feasibility experiments, we show that by modulating the polarization of a (T = 30 - 35 fs) long pulse, one can continuously control the harmonic pulse duration. The technique used for temporally modulating the ellipticity of a short pulse is simple and robust. By using two quartz plates, we can transform a pulse (of duration T) into a flat top pulse (duration 2 T) which is linearly polarized at the center (t=O) ofthe pulse and elliptically polarized at the begining and at the end of the pulse. The HHG is extremely sensitive to the ellipticity of the fundamental pulse and typically a 10% ellipticity reduces the efficiency by a factor 2. By temporally modulating the ellipticity of the fundamental pu1se;we therefore create a "gate" where the ellipticity is smaller than 10% inside which the harmonic emission is confined. In our experimental conditions, the minimum gate width is T / 6 (narrow gate). It can also be increased up to -2s (large gate) by rotating one of the plates. The high order harmonic pulse duration was estimated in two ways. In a first experiment (performed at the CELIA laboratory), the harmonic spectra were recorded and showed a clear dependance on the gate width. For the cutoff harmonics, the spectra broadened as the gate width was decreased as expected when a temporal confinment occurs. In contrast, for the plateau harmonics, the spectral width decreased with the gate width. Also counterintuitive, this is also consistent with a confinement because of the importance of the intensity dependent atomic,dipole phase. In both cases, the spectra were consistent with a confinement of the harmonic emission down to 5-7 fs. We could also observe that a temporal confinment does not always reduce the HHG efficiency and allows to optimize the phase matching. In a second experiment (performed at the Lund Laser Center), we measured directly the duration of harmonics created in Argon by doing a cross correlation of the harmonic pulse with an ultrashort (7-10 fs) 800 nin pulse. The cross correlation signal was the photoelectron peak corresponding to absorption of one harmonic photon plus absorption (or emission) of one photon of the ultrashort probe pulse. Because of a non-collinear geometry, the resolution of this measurement is larger than 10 fs but was sufficient to clearly observe an evolution of the harmonic pulse profile. For instance for the sideband 18 shown on the figure, the duration was 57 fs in the large gate configuration, 43 fs without any gate and 26 fs in the narrow gate situation. The confinment of HHG in the narrow gate configuration is therefore clearly visible, even for the plateau harmonics considered bere.